What Is an Additional Insured Endorsement? CG 20 10 Explained
The CertifiKit team
Certificate-of-insurance desk
An additional insured endorsement is a policy amendment that extends a subcontractor's or vendor's liability insurance to cover you — the hiring party — for claims arising out of their work. Without it, their insurer has no direct obligation to you, no matter what the certificate of insurance says. The most common form is CG 20 10 (ongoing operations), usually paired with CG 20 37 (completed operations).
Why does additional insured status matter?
Say your drywall sub damages a sprinkler line and floods two finished floors. If you're an additional insured on the sub's general liability policy:
- Their insurer defends you against the resulting claims, and
- The loss lands on their policy, not yours — protecting your loss history and premiums.
If you're not, you tender the claim to your own insurer, your premiums absorb the hit, and your insurer fights the sub's insurer for reimbursement. Same accident, very different year-end.
What do CG 20 10 and CG 20 37 actually cover?
| Form | Covers | When it matters |
|---|---|---|
| CG 20 10 | Liability arising from the sub's ongoing operations | Damage or injury while the work is happening |
| CG 20 37 | Liability arising from completed operations | The deck that fails six months after handoff |
| CG 20 38 / blanket forms | Anyone the named insured agreed in contract to add | Convenient, but read the contract-requirement wording |
Construction defect claims are overwhelmingly completed-operations claims — which is why requiring CG 20 10 alone is one of the most common gaps in subcontractor insurance requirements.
Is the checkbox on the COI enough?
No. The ACORD 25 certificate has an ADDL INSD checkbox, and agents check it as a courtesy summary. The checkbox is a claim; the endorsement attached to the policy is the fact. The certificate even says it confers no rights on the holder.
To actually verify additional insured status:
- Check the ADDL INSD box on the GL line — necessary, not sufficient.
- Look for the form number (e.g., "CG 20 10 04 13") in the description of operations.
- For meaningful contracts, request the endorsement page itself along with the certificate.
What's "primary and non-contributory"?
A companion requirement worth adding. By default, when two policies cover the same loss, insurers share it — meaning your policy still pays a slice. Primary & non-contributory wording makes the sub's policy pay first and prevents their insurer from asking yours to chip in. It typically appears as endorsement CG 20 01 or in the description of operations. A waiver of subrogation is the third clause worth requiring alongside it.
One more distinction worth nailing down before you file anything: being named additional insured is not the same as being the certificate holder — only one of them actually covers you.
How do I check all this on a real certificate?
Reading endorsement signals off an ACORD 25 means cross-checking checkboxes, the description-of-operations text, and form numbers — fiddly by hand, and easy to miss on certificate #47 of renewal season. (Our ACORD 25 field guide shows where everything lives.)
Or skip the squinting: upload the certificate to the free CertifiKit COI checker. It reads the endorsement signals along with limits and dates, compares everything against your requirements, and flags exactly what's missing — with the fix list written so you can forward it straight to the sub's insurance agent.